1. Field of the Invention
The present invention concern a spin disk apparatus and a method of use od said apparatus for coating biological materials such as tissues, cells and cell lines with a continuous, uniform, semi-permeable and bio-compatible coating. More particularly, this invention relates to a spin encapsulation apparatus and method for providing continuous uniform coatings of the biological material and other solid and semi-solid particles, to form smooth and uniform size microcapsules.
The apparatus comprises a particle suspension supply system, consisting of a container connected to a one or more centrally or off-center positioned needles and/or two or more concentrical needles positioned centrally or off-center, for storing the particles to be encapsulated in a coating polymer solution. The suspension supply system allows accurate metering of a suspension comprising particles to be coated and a coating polymer and introduction of the suspension onto the wall of a spinning beads forming cup of the spinning apparatus. The spinning apparatus further comprises a cup or disk for forming suspension droplets and projecting them outward from its central axis and into a collecting basin containing a gelling solution. The collecting basin surrounds the beads forming cup and is mounted for rotation about its central axis and positioned to collect droplets projected outward from the bead forming cup. The droplet forming cup and the collecting basin are independently connected to individual rotational motor drives having adjustable speeds. The needles of the supply system are positioned manually or, optionally, a conductivity data acquisition program/digital gauging probe system is used to determine and set the distance between dispensing needles and surface of bead forming cup.
2. Background Art and Related Art Disclosures
Coating or microencapsulation of solid particles in general, and biological materials in particular, is widely employed to protect the encapsulated substances from environmental effects, to control their release time, and to confer improved handling characteristics. Typical substances which are coated or microencapsulated are drugs and biological materials such as tissues, cells and cell lines.
Attempts to transplant organ tissues into genetically dissimilar hosts without immunosuppression have been generally defeated by the immune system of the host. The application of effective protective barrier coatings to isolate the transplant tissues from the host immune system has not proven to be medically practical for a number of reasons. The coating materials were incompatible with the host system or unsuitable for other reasons. Encapsulation or coating processes and apparatuses previously developed did not yield reproducible coatings having the desired permeability and thickness required for the transplant tissue to have a long and effective functioning life in the host.
To protect transplants from destruction by the immune response of the host animal, various attempts have been made to create a protective barrier between the transplant tissue or cells and the immunological components of the host's system. T. M. S. Chang, Science 146: 524-525 (1964) described the microencapsulation of erythrocyte hemolysate and urease in semi-permeable polyamide membranes. These microcapsules did not survive for long when injected into the blood stream. K. Mosbach et al, Acta Chem.Scand. 20:2807-2812 (1966) and T. M. S. Chang et al, Can.J.Physiol. and Pharmacology 44: 115-128 (1966) described the preparation of semi-permeable microencapsulated microbial cells and viable red blood cells, the latter article mentioning the possibility of using injections of encapsulated cells for organ replacement therapy.
Numerous other conventional coating or microencapsulation techniques have been developed. By and large, these techniques suffer from the inability to precisely control the thickness of the coating and the overall diameter of the microcapsules, while maintaining the ability to efficiently generate one or multiple coatings with smooth outer surfaces. The following patents exemplify these conventional techniques: U.S. Pat. No. 4,386,895 to Sodickson, U.S. Pat. No. 4,675,140 to Sparks et al., and U.S. Pat. No. 4,800,160 to Iguchi et al., and are hereby incorporated by reference.
The Sodickson patent discloses a capsule forming apparatus having an elaborate design of reservoirs and conduits. The capsule forming apparatus includes a rotor assembly which defines a gelling agent reservoir, and a rotor having a central axis of rotation. The rotor assembly is connected to a motor and a drive shaft. When the motor is actuated, the rotor assembly rotates about its axis. The rotor consists of a disc-shaped block having four radial vanes, and defines two concentric circular reservoirs and an opening coaxial to the rotor axis. A pair of conduits are spaced apart by 180 degrees adjacent to the bottom of the reservoir, for communication with two radial tubes. The reservoir and its associated conduits serve to replenish the gelling agent during the production of microcapsules.
Several radial conduits are disposed near the bottom of the reservoir, and communicate with a bundle of radial hollow needles. Four ducts are disposed next to the central opening and communicate with microcapsule-collecting tubes, and with yet another reservoir. The rotor assembly includes a vertical sidewall 68. In operation, the gelling agent is placed in the reservoir and a suspension is placed in the reservoir. When the rotor assembly is caused to rotate, the liquid gelling agent in the reservoir is centrifugally urged to form a layer 15-25 mm thick on the sidewall. Simultaneously, the gellable liquid and core material in the reservoir are centrifugally urged through the conduits and needles. As the liquid passes out of the needles, it breaks up into droplets which are propelled radially across a 2-5 mm gap to the layer of gelling agent, where they are gelled.
The Sparks et al. patent describes another method of coating particles by feeding a suspension of two materials onto a rotating disc. The suspension is centrifugally dispersed by the rotating disc into relatively small droplets of coating material. As the coated particles are dispersed by the rotating disc, they are solidified by exposure to air, and are separated by sieving. FIGS. 13-15 of the patent illustrate various conical and cup shaped forms of the rotary disc.
The Iguchi et al. patent describes a process and apparatus for producing immobilized enzyme granules, by forming drops of a gellable enzyme-containing liquid with a rotating disc, and bringing the drops in contact with a gelling solution. The disc is contained in a column, and the gelling solution flows down the walls of the column to a reservoir. Drops of the enzyme-containing liquid from the rotating disc contact the gelling solution while flowing down the walls and are carried to the reservoir.
Other encapsulation methods have comprised a procedure for forming droplets of the encapsulating medium and the biological material and a procedure for solidifying the encapsulating medium. Agarose encapsulated materials have been formed by chilling an emulsion of agarose droplets containing biological materials as shown by Nilsson et al, Nature 302:629-630 (1983) and Nilsson et al., Eur. J. Appl. Microbiol. Biotechnol. 17:319-326 (1983). Injection of droplets of polymer containing biological materials into a body of coolant such as a concurrently liquid stream has been reported by Gin et al, J.Microencapsulation 4:329-242 (1987).
Alginates form a gel when reacted with calcium ions. Alginate droplets have been formed by emulsifying a solution of sodium alginate containing cellular material to form droplets of sodium alginate and cells, and gelling the droplets with calcium chloride in U.S. Pat. No. 4,352,883. Alginate droplets have also been formed with a syringe and pump to force droplets from a needle, using a laminar flow air knife to separate droplets from the tip, the droplets being gelled by collecting them in a calcium chloride solution in U.S. Pat. No. 4,407,957. Alginate droplets have also been formed by the simple procedure of expelling them from a hypodermic needle and allowing the droplets to fall into a calcium chloride solution, as described by Nigam et al, Biotechnology Techniques 2:271-276 (1988).
Droplets have also been injected into a concurrently flowing stream containing calcium chloride in U.S. Pat. No. 3,962,383. Spraying alginate solutions through a spray nozzle to form a mist of droplets which were collected in a calcium chloride solution was reported by Plunkett et al, Laboratory Investigation 62:510-517 (1990). These methods have not proven effective for mass production of coatings having properties required for successful transplantation.
Hommel et al. in U.S. Pat. No. 4,789,550 disclose the formation of alginate droplets using a combination of a needle and a square wave electrical electrostatic voltage to form uniform droplets. The alginate solution is forced from the tip of a needle to form a droplet, and the droplet is pulled from the needle by a changing electrostatic field between the needle tip and a calcium chloride solution placed below the needle tip. The droplet receives a charge of one polarity from the needle, opposite to the charge in the calcium chloride solution. When the voltage difference between the droplet and the oppositely charged calcium chloride solution reaches a value at which the attraction by the solution on the droplet exceeded the force of interfacial tension holding the droplet on the needle tip, the droplet is pulled free to fall into the calcium chloride solution. The electrostatic field is fluctuated using a square wave form to create a succession of voltages crossing the threshold voltage at which droplets are pulled free from the needle, thus producing a continuous series of droplets, one per square wave cycle. The process is not found to provide the small droplets and thin coatings required for effective transplantation.
None of the above described art results in formation of microcapsules which have a small but uniform size, uniform thickness of coating and which does not produce substantial number of empty spheres.
Thus, there is still an unsatisfied need for new methods of preparing tissue transplants having properties needed for long-term survival of these transplants in human or animal body. There is, therefore, also a need for an encapsulation apparatus which efficiently produces transplants of the tissue coated with a single or multiple coatings with a high degree of size and thickness of coating control and reproducibility, at a rate to satisfy demands for transplant quantities.
All patents, patent applications and publications cited herein are hereby incorporated by reference.